Electron-discharge devices



Aug. 7, 1956 c. s. SZEGHO ELECTRON-DISCHARGE DEVICES Filed Dec 4 V/ Z//2 1 w Grid 3 M vo ooooooow oooooooooooooooomu W/////////////////////////U////U Q: OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOVCONSTANTIN A. SZEGHO PIC-5.1

IN V EN TOR.

HIS ATTORNEY.

United States Patent I O ELECTRON-DISCHARGE DEVICES Constantin S.Szegho, Chicago, Ill., assignor to The Rauland Corporation, acorporation of Illinois Application December 30, 1953, Serial No.401,127

Claims. (Cl. 315-3) The invention relates to electron-discharge devicesand more particularly to electron-discharge devices of the cathode-raytype suitable for use as image-reproducing devices in televisionreceivers.

Conventional electron-discharge devices of the cathoderay type comprisea substantially evacuated envelope enclosing a luminescent screen and anelectron gun for producing and accelerating an electron beam toward thescreen. The screen is normally composed of a coating of discretephosphor particles which emit light in response to electron bombardment,and is disposed upon the viewing surface of the envelope. deflectingsystems are employed to concentrate the electron beam and to deflect itin the formation of a twodimensional scanning pattern or raster upon thescreen. In the fabrication of such devices, a high degree of vacuum isproduced through the use of a mechanical evacuation means; a dispersionpump is commonly used for this purpose. It is well known that theefiic'iency of operation and the emission life of the electron sourcevaries with the degree of evacuation of the tube. Residual gas moleculesmay form positive and negative ions through bombardment by the electronbeam in its passage toward the screen, and since the cathode orelectron-emissive surface is normally at a negative potential withrespect to the other electrodes, the positive ions are propelled towardit and reduce the emission life by bombarding and physically displacingparticles of electron-emissive material.

In an eilort to meet this problem, a getter material is usuallyintroduced into the tube to absorb the gas molecules remaining aftermechanical evacuation. The getter material is normally distributedwithin the tube by flashing with an external source of energy such asradio-frequency electromagnetic radiation. In the flashing process thegetter material is heated to a temperature at which it vaporizes and isthus deposited in a thin film upon a large area of the enclosingenvelope. This technique of gettering is imperfect in many instancesbecause the one flashing may dispose of gas molecules present at thetime but it does effect the continuous absorption of additional gasmolecules which often times are released in the normal course ofoperation of the tube. In accordance with another technique, the getteris continuously energized by electric current during normal operation ofthe tube. Although the use of such a continuous getter results inprolonging the life of an electron-discharge tube, the maximumattainable extension of tube life is not realized be cause thecontinuous energization of the getter causes it to deteriorate at arelatively rapid rate.

It is an object of the present invention, therefore, to provide a newand improved electron-discharge device which avoids one or more of thedisadvantages of prior art structures.

It is a further object of the present invention to provide anelectron-discharge device in which the emission life of the electronsource is extended by more effective absorption of gas molecules throughthe action of a getter Suitable focussing and "ice material than hasbeen achieved by conventional practices.

It is yet another object of the present invention to produce anelectron-discharge device in which the tube life is extended byreplenishing the electron-emissive source with emissive materialreleased in the volatilization of the getter material.

In accordance with the invention, an electron-discharge device comprisesa substantially evacuated envelope including an electron gun having aplurality of electrodes and including a thermionic cathode. Anenergizing circuit is coupled to the cathode to cause electron emissionby heating the cathode. Additional energizing circuits are provided forapplying predetermined operating potentials to the other tubeelectrodes. A thermally responsive switch is mounted within the envelopein a position exposed to heat originating at one of the electrodes. Anelectrical circuit is coupled in parallel with one of the energizingcircuits and includes a conductive element of current-responsive gettermaterial supported within the envelope and connected in series with theswitch.

The features of the invention which are believed to be novel are setforth with particularity in the appended claims. The organization andmanner of operation of the invention, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in conjunction with theaccompanying drawing in theseveral figures of which like reference numerals indicate like elementsand in which:

Figure 1 is a fragmentary side elevation partly in cross section andpartly cut away, of an electron discharge device constructed inaccordance with the invention;

Figure 2 is a fragmentary view, similar to a portion of that of Figurel, of an alternative embodiment of the invention; and

Figure 3 is a top view, partly in cross-section of a portion of theillustrated embodiment of Figure 2.

The image-reproducing device of Figure 1 comprises a luminescent screen10 affixed to the glass targetportion 11 of an evacuated cathode-raytube envelope which also comprises a glass neck portion 12 enclosing anelectron gun and an electrostatic focussing system. The electron guncomprises a plurality of electrodes including a cathode 13. A heaterelement 40, which may be of any conventional construction such as ahelically'wound conductor, is disposed within cathode 13 and physicallymaintained in place by a spacing element 41 of suitable heat conductingbut electrically insulating material such as aluminum oxide. Conductiveleads 42 connect heater 40 to appropriate external pins 43 in the baseof the tube to constitute an energizing circuit to which an externalpotential source (not shown) is applied for the purpose of heatingcathode 13 to an emitting temperature.

The electron gun further includes a control electrode 14, and first andsecond tubular accelerating electrodes 15 and 16, respectively. Adiaphragm 17 having a central aperture 18 is disposed across the outletend of second accelerating electrode 16, and aperture 18 issymmetrically centered with respect to the tube axis A-A which isperpendicular to the center of the fluorescent screen 10. Electrode 16is laterally offset relative to electrode 15 to provide a steadytransverse electrostaticdetlection field component in the region betweenthese twoelectrodes, and the entire electron gun structure is tiltedwith respect to the tube axis AA by an angle p.

An electrostatic focussing system of the unipotential lens type isdisposed between the electron gun and the screen. The focussing systemcomprises the outlet end of electrode 16, a lens electrode 19, and anadditional electrode 20 which are all coaxially mounted with respect tothe tube axis A-A. Electrodes 19 and 20 may be provided with coronarings 33 and 35'. A centrally apertured conductive disc 21 is disposedin the neck portion oi the envelope between the focussing system andtarget portion 11. A conductive coating 22 of colloidal graphite, suchas aquadag or the like, extends from the direction of target portion 11into the neck portion of the envelope, and conductive disc 21 ismaintained at a common potential with conductive coating 22 by means ofmetal contact springs 23.

For convenience, electrodes 14, 15, 16, 19 and 20 may be termed gridsand may be designated by number starting with control electrode 14 asthe first grid and progressing in the direction of beam travel toelectrode 20 which is the fifth grid. All five grids are supported inpredetermined mutually spaced relation by means of nected to grids 3 andby means of metal strips 27. 9

Operating potential for the conductive coating 22, and therefore for thethird and fifth grids, may be supplied by means of a conventionalcontact button if the envelope is of the all glass type, or directly tothe metal cone if the tube' is of the glass-metal variety. In otherwords the electrode leads, basing pins or high-voltage terminals provideenergizing circuits for applying operating potentials to the electrodesystem of the tube.

An external permanent magnet 28, supported in a spring clamp 29 whichfits snugly around the neck of the tube and is movable both axially androtationally, is provided to develop a magnetic field within the tube toprovide separation of the negative ions from the electron beam.

The tube is evacuated, sealed and based in accordance with well knownprocedures and suitable getters 31 are supported from the surface ofconductive disc 21 facing fluorescent screen to absorb residual gasesafter evacuation.

The structure as thus far described is a well-known cathode-ray tube andthe details of its electrode system as well as its operation indeveloping a beam of electrons,

v 4 The trough of element 44 is filled with a current responsivegettermaterial 45, which preferably consists of an alloy of barium; however,other commercial products such as alloys of magnesium or calcium, may beemployed.

Suitable getter materials may be composed of any of the followingmixtures of barium, aluminum and magnesium or other convenientpercentages of these elements: Ba 25%, Mg Al'20%', Ba 37%, Mg. 37%, Al26%; Ba 43%, Mg 20%, Al 37. Metallic barium would be preferable to analloy except for its instant reaction to gaseous molecules or to gaseousvapors present in the air. The use of an alloy of barium has anadvantage in that in this form barium is inert, but may be energized byflashing. Another getter material that may be used is a carbonate oroxide of barium which is reduced to barium by outgassing at atemperature lower than that of the flashing temperature. In the lattercase a temperature of 800 to 1100 degrees centigrade reduces the bariumcompound to yield about 40% barium. By flashing at a higher temperature,usually inthe range of 1200 to 1300 degrees centigrade, the barium actsas a getter in the well known manner.

A normally-closed thermally responsive switch 46, preferably of thebimetallic type, is connected in series with element 44 and ispositioned adjacent to electrode 14. Switch 46 may comprise anythermostatic structure known in the art which makes or breaks anelectrical circuit in response to its attaining a predeterminedtemperature. Such switches are composed of two metals having differenttemperature coefiicients affixed to one another to distort away from andopen a contact upon the application of heat. Frequently, a strip ofnickel and a strip of copper are employed although other combinations ofdissimilar metals are equally satisfactory. It has been found thatsufiicient heat is generated by the cathode structure, which may attainan operating temperature in the vicinity of 800 degrees Centigrade, toactuate switch separating unwanted ions from the beam, and projectingthe purified beam toward the luminescent screen are well understood.They are described in particular, for example, in U. S. Patent No.2,658,160, issued November 3, 1953, in the name of Russel S. Peterman,and assigned to the same assignee as the present invention. The detailsof corona rings 33 and 35 and their function in the tube are describedand claimed in a copending applicar tion of Constantin S. Szegho, SerialNo. 229,013, filed May 31, 1951, now U. S. Patent 2,673,305, andassigned to the same assignee.

In order to extend the useful life of the tube,

recognizing that conventional gettering techniques utilizing pellets 31may not adequately protect against the possibility of occluded gases,the present invention provides an improved gettering structure. Morespecifically,

an electrical circuit including a conductive element 44 convenientlywound in contact with the surface of electrode 14, it may be insulatedtherefrom by simple spacers of electrically non-conducting material, asfor example, aluminum oxide or the like. Of course, in either case thesupport for element 44 may be grooved to strengthen the assemblymechanically. In addition, element 44 may be wound around and supportedby glass supports 24.

46 and the positioning of the switch is not critical so long as duringthe operation of the tube the elements of the switch achieve thetemperature at which the switch opens. A shield 48, which may be a smallpiece of sheet metal welded to electrode 14 and disposed between getter45 and glass support 24, prevents volatilized getter material from beingdeposited upon the surface of the glass support and causing a shortcircuit between some of the gun electrodes.

In explaining the operation of the described getter circuit, it may beassumed that the tube is'incorporated into suitable apparatus; forexample, it may serve as the image-reproducing device of a televisionreceiver. To operate the tube in any such environment, energizingpotentials are applied to its several electrodes. Concurrently with theapplication of such energizing potentials. current How is initiatedthrough the getter circuit since it is connected in parallel with thefilament of the cathode. The flow of current through element 44generates sufficient heat in this element to vaporize getter material 45which in the art is referred to as flashing the getter. The actuation ofthe getter causes any undesirable gas molecules present in the tube tobe absorbed in the usual manner and the activation of the gettercontinues until such time as switch 46 of the getter circuit is opened.After a relatively short interval, the energizing potentials applied tothe electrode systems of the tube raise the cathode structure inparticular to an operating temperature which, as has been described, issufficiently high to open switch 46. At this point, current no longerflows in the getter circuit.

When the electron-discharge device is turned off, electrode 14 returnsto ambient temperature, resulting in the closure of the contacts ofbimetallic switch 46. Upon reenergization of the electron-dischargedevice, however, another, cycle of the above-described operation isbegun and the getter material vaporizes further to absorb any 5 residualgas molecules. Since during the normal operation of the tube occludedgas molecules are liberated from many areas, particularly fromfluorescent screen 10, it is advantageous to re-energize the getter inthis cyclic fashion to prolong the life of the tube.

It has been found that if the emissive coating of cathode 13 is composedof metallic barium and if the getter material is also composed of apreponderance of barium, an additional extension of the emissivc life ofcathode 13 may result. Apparently, the barium coating upon the surfaceof cathode 13 is replenished in part by molecules of the barium gettermaterial when itis volatilized. It would appear that because of randommovement the mole cules of barium from the getter are deposited uponcathode 13 to replace the electron-emissive coating depleted by normaltube operation.

The full benefits of the invention are not realized if the gettermaterial completely flashes upon the first application of current toelement 44. Protection against ex hausting the getter at the firstflashing may be attained by employing as conductive element 44 atubethat is substantially continuous in cross section but is so thinin wallthickness as to be porous and hence partially pervious to barium vapor.With such a construction the getter material is not completely vaporizedin any one cycle of operation; instead a substantial portion is retainedwithin the tube from one flashing to the next. Alternatively, theenclosing tube may be impervious to vapors of the getter material exceptfor a narrow section that may be slotted, perforated or otherwiserendered pervious to the getter vapor to permit vaporization of thegetter in a controlled manner and to direct the vapor over apredetermined area of tube neck 12. Such a construction is representedin the embodiment of Figures 2 and 3, which is identical in function andstructure to that of Figure 1 except that conductive element 44'entirely encloses the getter material and further, instead of beingwound externally of electrode 14, in this embodiment it is disposedupwardly in the neck or" the cathode-ray tube. In this latterarrangement, getter material 45 may be deposited over a greater area ofneck 12 resulting in a more efficient absorption of residual gasmolecules. In this embodiment conductive element 44' enclosing thegetter material is mechanically supported by rigid spacers 50 and 51inserted into supports 2 and extends into the neck portion 12 of thecathode-ray tube longitudinally alon these supports. Perforations 52.are disposed along the longitudinal surface of element 44 to permitcontrolled vaporization of the enclosed getter. Electrical terminationsare connected to one filament lead of heater element 40 and to grid 2.The energizing current whi h heats element 44 to volatilize the gettermaterial is produced by the potential difference between grid 2 which isusually maintained at B+ and the grounded side of the filament lead toheater element 40. Although this arrangement may be suitable forpractical re-energization of the getter material in cyclic fashion,conductive element 44 may be advantageously wound spirally about thesurface of grid 3 provided it is maintained therefrom by insulatingspacers (not shown). The particular configuration of the getter supportstructure is shown for purposes of illustration only and should not beconsidered a limitation upon the subject invention.

In addition, although switch 46 may be conveniently operated by heatgenerated in the cathode structure, it may also be operated by heatgenerated in other portions of the tube. A simple proportioning of thethickness of one of the metallic strips comprising the bimetallicelements permits an adjustment of the radius of curvature formed by thedistortion of the armature of the switch in response to heat. in theusual case the bias necessary to make positive electrical contact may beenhanced by a mechanical spring in the manner well known in the art. Asan illustration of another of the possible operating positions of switch46, Figure 2 shows it disposed in the 6 vicinity of diaphragm 17 of grid3. This area of the tube is heated by electron bombardment upon thesurface of diaphragm 17. Switch 46 maintained in position by metal rods55 and 56 mechanically and electrically connecting it to element 44 asillustrated in Figure 3, a top view taken along line 33 of Figure 2.

Therefore the present invention discloses a new and improvedelectron-discharge device which includes a builtin provision forextending life of the cathode by momentarily actuating a getter materialautomatically each time the device is placed in normal use. It isthrough a simple structural addition that the residual gas moleculesremaining within the envelope and liberated in the course of normaloperation are absorbed to prolong the useful tube life. In addition, aneven greater extension of tube life may be realized by employing anappropriate getter material to replenish the electron-emissive materialfrom time to time with molecules of volatilized getter which upondeposition also become electron-emissive. Further the cyclic operationof applicants invention prolongs the effective life of the getter beyondthat usually found in the use of a continuous getter which is rapidlydissipated.

While particular embodiments of the invention have been shown anddescribed, modifications may be made and it is intended in the appendedclaims to cover all such modifications as may fall Within the truespirit and scope of the invention.

I claim:

1. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathodesupported within said envelope; an energizing circuit for heating saidcathode to cause electron emission therefrom; additional energizingcircuits for applying predetermined operating potentials to saidelectrodes; a thermally responsive switch mounted within said envelopein a position exposed to heat originating at one of said electrodes; andan electrical circuit coupled in parallel with one of said energizingcircuits and including a conductive element of current-responsive gettermaterial supported Within said envelope and connected in series withsaid switch.

2. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathodesupported within said envelope; an energizing circuit for heating saidcathode to cause electron emission therefrom; additional energizingcircuits for applying predetermined operating potentials to saidelectrodes; a normally-closed thermally responsive switch mounted withinsaid envelope in a position attaining at least a predeterminedtemperature in normal operation of said device and adapted to open uponattaining said predetermined temperature; and an electrical circuitcoupled in parallel with one of said energizing circuits and including aconductive element of current responsive getter material supportedwithin said envelope and connected in series with said switch.

3. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathodesupported within said envelope; an energizing circuit for heating saidcathode to cause electron emission therefrom; a normally-closedthermally responsive switch mounted within said envelope in a positionattaining at least a predetermined temperature in normal operation ofsaid device and adapted to open upon attaining said predeterminedtemperature; and an electrical circuit coupled in parallel with saidenergizing circuit and including a conductive element ofcurrent-responsive getter material supported within said envelope andconnected in series with said switch, whereby said getter material ismomentarily activated each time normal operation of saidelectron-discharge device is initiated.

4. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathode and acontrol grid supported within said envelope; an energizing circuit forheating said cathode to cause electron emission therefrom; additionalenergizing circuits for applying predetermined operating potentials tosaid electrodes; a thermally responsive switch mounted adjacent saidcontrol grid in a position exposed to heat emanating from said controlgrid; and an electrical circuit coupled in parallel with one of saidenergizing circuits and including a conductive element ofcurrent-responsive getter material supported within said envelope andconnected in series with said switch.

5. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathode andan accelerating anode supported within said envelope; a first energizingcircuit for heating said cathode to cause electron emission therefrom;additional energizing circuits for applying predetermined operatingpotentials to said electrodes; a thermally responsive switch mountedWithin said envelope in a position exposed to heat originating at one ofsaid electrodes; and an electrical circuit coupled between saidaccelerating anode and said first energizing circuit and including aconductive element of current-responsive getter material supportedwithin said envelope and connected in series with said switch.

6. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathodesupported within said envelope; an energizing circuit for heating saidcathode to cause electron emission therefrom; additional energizingcircuits for applying predetermined operating potentials to saidelectrodes; a thermally responsive switch mounted within said envelopein a position exposed to heat originating at one of said electrodes; anelectrically conductive element of semitubular cross-section partiallyenclosing current-responsive getter material supported within saidenvelope; and an electrical circuit coupled in parallel with one of saidenergizing circuits and including said electrically conductive elementand connected in series with said switch.

7. An electron-discharge device having a longitudinal dimensionalgreater than its transverse dimension and comprising: a substantiallyevacuated envelope; a plurality of electrodes including a thermioniccathode, all

maintained in fixed relationship within said envelope by 1 a pluralityof supporting elements; an energizing circuit for heating said cathodeto cause electron emission therefrom: additional energizing circuits forapplying predetermined operating potentials to said electrodes; athermally responsive switch mounted within said envelope in a positionexposed to heat originating at one of said electrodes; an electricallyconductive element of substantially circular cross-section mechanicallymaintained in a predetermined position by at least one of saidsupporting elements along said longitudinal dimension and partiallyenclosing current-responsive getter material supported within saidenvelope; and an electrical circuit coupled in parallel with one of saidenergizing circuits, including said electrically conductive element andconnected in series with said switch.

8. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathodesupported within said envelope; an energizing circuit for heating saidcathode to cause electron emission therefrom; additional energizingcircuits for applying predetermined operating potentials to saidelectrodes; a thermally responsive switch mounted Within said envelopein a position exposed to heat originating at one of said electrodes; anelectrically conductive element of semitubular cross-section woundspirally around one of said electrodes and partially enclosingcurrent-responsive getter material supported within said envelope; andan electrical circuit coupled in parallel with one of said energizingcircuits and including said electrically conductive element andconnected in series with said switch.

9. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathode andan accelerating anode supported within said envelope; an energizingcircuit for heating said cathode to cause electron emission therefrom;additional energizing circuits for applying predetermined operatingpotentials to said electrodes; a thermally responsive switch mountedwithin said envelope in a position exposed to heat originating at saidaccelerating anode; and an electrical circuit coupled in parallel withone of said energizing circuits and including said electricallyconductive element and connected in series with said switch device.

10. An electron-discharge device comprising: a substantially evacuatedenvelope; a plurality of electrodes including a thermionic cathodesupported within said envelope and comprising an electron emissiveelement of barium; an energizing circuit for heating said cathode tocause electron emission therefrom; additional energizing circuits forapplying predetermined operating potentials to said electrodes; athermally responsive switch mounted within said envelope in a positionexposed to heat originating at one of said electrodes; and an electricalcircuit coupled in parallel with one of said energizing circuits andincluding a conductive element of current-responsive getter materialcomprising barium supported within said envelope and connected in serieswith said switch.

References Cited in the file of this patent UNITED STATES PATENTS1,739,043 Ruben Dec. 10, 1929 1,787,300 Alexanderson Dec. 30, 19302,392,969 Bickley Jan. 15, 1946 2,575,835 Pohle Nov. 20, 1951 2,638,559Giacchetti May 12, 1953 2,668,253 Taylor Feb. 2, 1954

